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LSF0102: Questions of LSF0102

Jimmy Lai
Expert 6845 points
Part Number: LSF0102
Other Parts Discussed in Thread: TXS0102

Dear Team,

Currently, there is a case where LSF0102DCTR is used and the signal high level of Port B does not reach the voltage of Vref_B (4.2V), only about 2.2~2.3V.
The Port B signal is connected to TLC59208FIPWR. Even after adjusting the resistance of R45 and R48 & R49 to a smaller value, the same problem remains. Can you please help confirm which side of this part is the problem? Thank you.

Many Thanks,

Jimmy

  • 0
    Guru 297840 points

    The device that is driving the lines low must be able to sink the current through all pull-up resistors. What is that 1.8 V device? What is its drive strength?

  • 0 in reply to Clemens Ladisch
    TI__Expert 6845 points

    Hi Clemens,

    The 1.8V side is an open-drain configuration of the QUALCOMM CPU, so the drive current flows through the pull-up resistors.
    We have tried to change the pull-up resistors on the 4.2V and 1.8V sides to 1K, but this did not improve the I2C signal voltage on the 4.2V side.

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    Guru 297840 points

    What model is that CPU? What is the drive strength of its I²C pins?

  • 0 in reply to Jimmy Lai
    TI__Mastermind 30946 points

    Hi Jimmy,

    In addition to Clemens' response, please provide the non-functioning waveform for further debugging. You may also see the TXS0102 that contains internal one shot circuitry to help accelerate the rising edge to the desired output voltage.

    Regards,

    Jack 

  • 0 in reply to Clemens Ladisch
    TI__Expert 6845 points

    Hi Clemens,

    The CPU is the QUALCOMM X75 model, and we have tried the 2mA and 16mA configuration settings for the I2C pins, but the results on the 4.2V side were the same.

    Many Thanks,
    Jimmy

  • 0 in reply to Jimmy Lai
    Guru 297840 points

    When the I²C bus is idle, no current should flow. Are there any other devices connected to the I²C lines that could pull them low? Please check for shorts to GND.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 30946 points

    Hi Jimmy,

    Clemens' is correct here- please check if there is are any external pulldowns that are not shown on the schematic or if there are any leakage paths.

    Regards,

    Jack 

  • 0 in reply to Jack Guan
    TI__Expert 6845 points

    Hi Jack,

    The I2C bus was only connected to the TLC59208FIPWR, so there were no other devices to pull the bus low. The I2C bus NACK waveform on the 4.2V side is shown below:

    However, I have replaced the LSF0102DCTR with dual MOSFETs, and it has the correct waveform. Therefore, I suspect that the port B internal sink current of the LSF0102DCTR is not able to pull up to high voltage.

    Many Thanks,

    Jimmy

  • 0 in reply to Jimmy Lai
    Guru 297840 points

    There is no internal sink current; the LSF uses the same MOSFETs. This looks as if there was a solder bridge somewhere.